diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright Chris Done (c) 2018
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Chris Done nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,63 @@
+# caseof
+
+A simple way to query constructors, like cases but slightly more
+concise.
+
+Aimed at sum types with many constructors:
+
+``` haskell
+data Wiggle = Woo Int Char | Wibble Int deriving Show
+```
+
+There is a case predicate:
+
+``` haskell
+> $(isCaseOf 'Woo) (Woo 5 'a')
+True
+```
+
+There is a `Maybe`-based matcher:
+
+``` haskell
+> $(maybeCaseOf 'Woo) (Woo 1 'a')
+Just (1,'a')
+```
+
+There is a combinator which calls your function with n arguments, or
+passes the whole value to an "else" clause.
+
+``` haskell
+> $(caseOf 'Woo) (\x y -> show x ++ show y) (const "") (Wibble 5)
+""
+```
+
+This allows them to be nested:
+
+```haskell
+> $(caseOf 'Woo) (\x y -> show x ++ show y) (const "") (Woo 5 'a')
+"5'a'"
+> $(caseOf 'Woo) (\x y -> show x ++ show y) ($(caseOf 'Wibble) show (const "")) (Woo 5 'a')
+"5'a'"
+```
+
+What's the point of `caseOf`? To more easily dispatch on functions:
+
+```haskell
+handleHuman name age = ...
+handleMachine id = ..
+handleWithDefault def =
+   $(caseOf 'Human) handleHuman .
+   $(caseOf 'Machine) handleMachine def
+```
+
+This applies to any kind of "case" that you'd like to refactor into a function.
+
+## Use in your project
+
+In your stack.yaml, put:
+
+```
+extra-deps:
+- git: https://github.com/chrisdone/caseof.git
+  commit: 9a7f6bb
+```
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/caseof.cabal b/caseof.cabal
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--- /dev/null
+++ b/caseof.cabal
@@ -0,0 +1,25 @@
+name:                caseof
+version:             0.0.0
+synopsis:            Combinators for casing on constructors
+description:         Template-Haskell-based combinators that let you select on constructors.
+homepage:            https://github.com/chrisdone/caseof#readme
+license:             BSD3
+license-file:        LICENSE
+author:              Chris Done
+maintainer:          chrisdone@gmail.com
+copyright:           2018 Chris Done
+category:            Development
+build-type:          Simple
+extra-source-files:  README.md
+cabal-version:       >=1.10
+
+library
+  hs-source-dirs:      src
+  ghc-options:         -Wall
+  exposed-modules:     CaseOf
+  build-depends:       base >= 4.7 && < 5, template-haskell
+  default-language:    Haskell2010
+
+source-repository head
+  type:     git
+  location: https://github.com/chrisdone/caseof
diff --git a/src/CaseOf.hs b/src/CaseOf.hs
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--- /dev/null
+++ b/src/CaseOf.hs
@@ -0,0 +1,81 @@
+{-# OPTIONS_GHC -fno-warn-type-defaults #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE TemplateHaskell #-}
+
+module CaseOf where
+
+import Language.Haskell.TH
+import Language.Haskell.TH.Syntax
+
+-- | Create a predicate that returns true if its argument is the given constructor.
+isCaseOf :: Name -> Q Exp
+isCaseOf input = do
+  name <- nameAsValue input
+  pure
+    (LamCaseE
+       [ Match (RecP name []) (NormalB (ConE 'True)) []
+       , Match WildP (NormalB (ConE 'False)) []
+       ])
+
+-- | Return Just (x, y, ..) for the constructor C x y .., or Nothing.
+maybeCaseOf :: Name -> Q Exp
+maybeCaseOf input = do
+  name <- nameAsValue input
+  info <- reify name
+  case info of
+    DataConI _ ty _ ->
+      pure
+        (LamCaseE
+           [ Match
+               (ConP name (map patI [1 .. arity ty]))
+               (NormalB (AppE (ConE 'Just) (TupE (map varI [1 .. arity ty]))))
+               []
+           , Match WildP (NormalB (ConE 'Nothing)) []
+           ])
+    _ -> fail ("Invalid data constructor " ++ pprint input)
+  where
+    varI i = VarE (mkName ("v" ++ show i))
+    patI i = VarP (mkName ("v" ++ show i))
+    arity (ForallT _ _ t) = arity t
+    arity (AppT (AppT ArrowT _) y) = 1 + arity y
+    arity _ = 0
+
+-- | Call a function with arguments from the constructor if it
+-- matches, or pass it to the wildcard function.
+caseOf :: Name -> Q Exp
+caseOf input = do
+  name <- nameAsValue input
+  info <- reify name
+  case info of
+    DataConI _ ty _ ->
+      pure
+        (LamE [VarP f, VarP nil]
+           (LamCaseE
+              [ Match
+                  (ConP name (map patI [1 .. arity ty]))
+                  (NormalB (foldl AppE (VarE f) (map varI [1 .. arity ty])))
+                  []
+              , Match (VarP this) (NormalB (AppE (VarE nil) (VarE this))) []
+              ]))
+    _ -> fail ("Invalid data constructor " ++ pprint input)
+  where
+    f = mkName "f"
+    this = mkName "this"
+    nil = mkName "nil"
+    varI i = VarE (mkName ("v" ++ show i))
+    patI i = VarP (mkName ("v" ++ show i))
+    arity (ForallT _ _ t) = arity t
+    arity (AppT (AppT ArrowT _) y) = 1 + arity y
+    arity _ = 0
+
+-- | Return the name if it is a value constructor, otherwise lookup a
+-- value name.
+nameAsValue :: Name -> Q Name
+nameAsValue name =
+  if nameSpace name == Just DataName
+    then pure name
+    else do
+      mname <- lookupValueName (nameBase name)
+      case mname of
+        Nothing -> fail ("Not in scope constructor " ++ pprint name)
+        Just n -> pure n